Using Analog Meters in Your Projects

These days, we are used to deploying sophisticated displays in our electronic systems, such as full text (with multiple, easy-on-the-eye fonts) and full graphics liquid crystal displays (LCDs). In the not-so-distant past, however, display technologies were much more limited.

Prior to the arrival of the first visible spectrum light-emitting diodes (LEDs) in the early 1960s, the majority of displays were either analog, in the form of meters, or digital, in such forms as on/off indicator bulbs or -- if you really wanted to be flashy (no pun intended) -- Nixie Tubes (see also Outrageously Awesome Nixie Tube Clocks and The Art of Hand-Crafting Nixie Tubes).

Now, some people will say that digital displays are quicker and easier to read than their analog cousins, but this is not necessarily the case. Imagine a wall of analog meters in a nuclear power station, for example. A simple scan will quickly tell you if their needles (pointers) are in their safe, warning, or danger zones.

Another thing you commonly hear is that that digital displays are more accurate and precise than their analog counterparts, but the accuracy and precision of any data being displayed depends not only on the display mechanism (how big is your analog meter or how many digital digits are at your disposal, for example), but also on the way in which that data is gathered and processed prior to being displayed.

Quite apart from anything else, I like using analog meters for my hobby projects because they offer a sense of "je ne sais quoi." Now, some people choose to use modern analog meters for their creations, but I prefer to employ antique devices that I pick up at electronic flea markets (like the local Huntsville Hamfest) or rescue from old equipment because they have a certain something about them.

Huntsville Hamfest (Source: Max Maxfield)

Ooh...shiny! (Source: Max Maxfield)

To provide you with an example, one of my ongoing hobby projects is something I call my Vetinari Clock. This name derives from the character Lord Havelock Vetinari who appears in Terry Pratchett's Discworld series of books. Lord Vetinari has a strange clock in his waiting room. Although it keeps accurate time overall, it sometimes ticks and tocks out of sync: "tick, tock, tick, tock…tick-tick-tock-tick…tock…" By the time your audience with Lord Vetinari is granted, your nerves are totally frazzled, thereby placing you at a grave disadvantage.

In the case of my clock, I decided to use four meters -- a big one for the hours, two medium-size devices for the minutes and seconds, and a small unit to act as a mini-metronome reflecting the passing of the seconds. (I'm also planning on adding audio effects that will allow the inner working of my clock to sound like clockwork, or pneumatics, or even use the sound of dripping water to indicate the passing of time.)

My graphic artist chum, Denis Crowder (based in Hawaii), very kindly designed a consistent set of faceplate graphics for me, then another friend, John Strupat (based in Canada), fabricated the faceplates using a process he's developed himself. The results are as shown below.

(Source: Max Maxfield)

You have to admit that these do look rather spiffy. The next thing was to decide how to present these meters to the world. I pondered, reflected, cogitated, and ruminated about this for hours, sketching out all sorts of different configurations. Eventually, I made my decision; the result is shown below.

(Source: Max Maxfield)

Note that this is just a rough mockup of the front panel created using 1/4" thick MDF (medium-density fibreboard). In the real version, this front panel is going to feature an amazing wood veneer with an aluminum look-and-feel (click here to see an image of this veneer). Meanwhile, the surrounding cabinet will be 0.5" thick and made of ebony (or, more likely, ebonized pear wood because that's much cheaper, or possibly even regular wood with an ebony veneer).

Now, I should warn you that there can be some drawbacks to using antique analog meters, not the least being that these are sealed units that are not intended to be opened by the hoi polloi* lest dust and other contaminants get in. Also, when it comes to creating the electronics to drive these little rascals, you need to know the resistance of the meter's coil. The problem here is that attempting to use a digital multimeter to measure this resistance may blow the coil and render the meter unusable.

*Yes, I know that hoi polloi (which I'm taking to mean "the great unwashed") comes from the Ancient Greek, meaning "the many," so some linguistic prescriptivists (a.k.a. people who don't get invited to many parties) argue that saying "the hoi polloi" is redundant as it's akin to saying "the the masses." However, this is inconsistent with other English loanwords, "the hoi polloi" sounds better to my ear, and I'm the one writing this article, so I get to choose -- QED.

I'll be telling you more about this clock and the problems (and solutions) associated with using antique analog meters in a future column. In the meantime, as always, I welcome your questions and comments.

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Speaking of analog meters, I have some for sale...
These were rescued from the estate of a ham radio operator and are mostly similar to those you picked up at the Huntsville hamfest. There are a couple unique ones though. It doesn't look like there's any way for me to post pictures here so I'll send them to you.

Just wondering if you have had any thoughts about using the big meter I sent you a while ago. I know there's not enough hours in the day - can you modify your time reference relative to the rest of us so you can get more done?

@Elizabeth: "...there are a couple unique ones though. It doesn't look like there's any way for me to post pictures here so I'll send them to you..."
Hi Elizabeth -- you can email images to me at my max@clivemaxfield.com account

@Ian Johns: "...Just wondering if you have had any thoughts about using the big meter I sent you a while ago..."
Hi Ian -- it's still sitting here in my office -- I have lots of ideas for different projects based around this beauty -- but I have zero free bandwidth to implement them at the moment (sob sob)

Old Analog meters are indeed good things. Someone just gave me 5 - a 300V meter, 3 x 50A Ammeters, and a vibrating reed frequency meter. This last let you estimate the mains frequency - probably to within about 0.25 Hz or less - via a set of vibrating reeds all resonant at different frequencies between 47 and 53 Hz (I come from 50Hz land). Not sure what I will use the 50A meters for, and they are Moving Iron so not easy to adapt to different sensitivities.

@David: "...This last let you estimate the mains frequency - probably to within about 0.25 Hz or less - via a set of vibrating reeds all resonant at different frequencies between 47 and 53 Hz..."
OMG I would love to see this in action -- the folks of yesteryear were incredibly inventive.

Ian's is not quite as pretty as mine. I was wondering what the large box in series was, but with the aid of Google translate I determined that it was an "Additional resistor for frequency meter" (in Polish). (Insert joke about reverse polish notation here :-) Mine does not need a resistor.

@Max.... "@David: "...Mine does not need a resistor..."
I don't know why, but I imagine you sneering when you say this LOL
Of course. One-upmanship is alive and well :-)
I'd also love to know how Ian posts videos. I can't even post a pic...

@Max, David - re posting of videos, the EEWeb must be cleverer than we think. All I did was copy the url of the video into this comment box. The address just appears as a text string but the EEWeb site must scan the text, recognise that there is an url address, open it & insert the video.